johnk@olg.com
Cadet
- Joined
- Feb 19, 2002
- Messages
- 7
Re: Low speed at deep waters
I guess you have to see it to believe it but planing boats really can speed up in shallow water. my explanation is that as the boat moves along pushing the water out of the way of itself, in shallow water the displaced water hits the bottom and builds up extra pressure under the boat. This causes the boat to raise a little more, you have less wetted area, less friction, greater speed. <br /><br />Ever go to the ocean shore and see kids using a skim board? Its a round flat board about 2 ft across. You throw it down on the 1 or 2 inch layer of water left that starts to run back down the beach after a wave breaks on the beach. They jump on the board and skim across the beach like ther was no friction. Its not bouyancy holding up the weight because this does not work in deep water. When the board is going fast enough, the water does not have enough time to get out of the way. The water gets - hold on to your hats - compressed a little bit and provides enough pressure to support the weight of a person. I believe the same type of thing happens to planing boats to a smaller degree. It seems to have the biggest effect in flat bottom boats.
I guess you have to see it to believe it but planing boats really can speed up in shallow water. my explanation is that as the boat moves along pushing the water out of the way of itself, in shallow water the displaced water hits the bottom and builds up extra pressure under the boat. This causes the boat to raise a little more, you have less wetted area, less friction, greater speed. <br /><br />Ever go to the ocean shore and see kids using a skim board? Its a round flat board about 2 ft across. You throw it down on the 1 or 2 inch layer of water left that starts to run back down the beach after a wave breaks on the beach. They jump on the board and skim across the beach like ther was no friction. Its not bouyancy holding up the weight because this does not work in deep water. When the board is going fast enough, the water does not have enough time to get out of the way. The water gets - hold on to your hats - compressed a little bit and provides enough pressure to support the weight of a person. I believe the same type of thing happens to planing boats to a smaller degree. It seems to have the biggest effect in flat bottom boats.